1. Field of the Invention
The present invention relates to optical pickups, and more particularly to an optical pickup and method of adjusting same used to read information from an optical disc (hereinafter merely referred to as "disc"), such as CD and DVD.
2. Description of the Prior Art
There is disclosed one example of a conventional optical pickup of this kind in Japanese Patent Publication No. H5-9851. This conventional art has a diffraction element 3 to cause diffraction in a main beam reflected from a disc 6 and split it into two. These diffracted beams are converged onto regions 7a, 7b and 7c of a light receiving element 7 so that the difference (Sa-Sb) in output signal of between the regions 7a and 7b provides a focusing error signal while the sum (Sa+Sb+Sc) of the output signals from the areas 7a, 7b and 7c gives a pit signal.
In such an optical pickup, the adjustment in positional relationship between the diffraction element 3 and the light receiving element 7 requires actual rotation of the disc 6 to perform focusing servo using a servo circuit. The diffraction element 3 is displaced such that the jitter value observed by a jitter meter is brought to a best.
In the conventional optical pickup, however, there has been a problem that the adjustment is troublesome and consumes a long time, because it requires actual rotation of a disc 6 in order to implement focussing servo. Also, there has been another problem that the provision of the servo circuit results in mounting-up of cost. Moreover, there has been still another problem that the optical pickup is difficult to stabilize its characteristics, because the displacement of the diffraction element is based on a jitter value as a reference that is susceptible to noises.